Noradrenergic Receptor Blockade of the NTS Attenuates the Mnemonic Effects of Epinephrine in an Appetitive Light–Dark Discrimination Learning Task

Abstract

These experiments examined the contribution of noradrenergic neurons in the nucleus of the solitary tract (NTS) in mediating the memory-facilitating effects of epinephrine. In Experiment 1, saline or 0.05 or 0.1 mg/kg of epinephrine was given intraperitoneally (ip) to rats after the second day of training in a light-dark Y-maze discrimination task. On a 20-trial retention test given 2 and 7 days later, the 0.1 mg/kg epinephrine group made significantly more correct responses than controls and required fewer trials to reach criterion. In Experiment 2, phosphate-buffered saline or the noradrenergic antagonist dl-propranolol (0.3 or 1.0 μg/0.5 μl) was infused into the NTS prior to an ip injection of saline or 0.1 mg/kg of epinephrine. The memory-enhancing effects of epinephrine were attenuated by the infusion of 0.3 μg/0.5 μl of dl-propranolol into the NTS. These findings indicate an involvement of NTS noradrenergic neurons in mediating the effects of peripheral epinephrine on memory storage processes.